Many researchers debate about the origin of life on earth. The sciencist Miller provided with an empirical experiment, that the main compounds of enzymes, called amino acids, emerge under conditions in the early atmosphere.
Miller got the idea to simulate the processes in the prehistoric atmosphere in a very small scale. All he used was water, common gases and electric charge. The water was boiled and its evaporation mixed with different gases like Methan (you could add one or two gases). In the enclosed reactor this mixture of gases was striked by continuous electrical charges, which seems to occur in the early atmosphere. A partial cooling area at the top of the reactor condensed the water vapour, so that it dropped back to the ground where it was heated again.
After a short time Miller found organic molecules and even amino acids in the solution. He assumed that these basic structures originated life on earth.
The quality of the Miller-experiment had been debated sceptically for a long time. In his lecture the professor casts doubt on its value and gives some examples for critics.
First, Miller reduced oxygen of his reproduced atmosphere. Many people were concerned about this, since the absence of one compound diminishes or even denies the result of the whole experiment.
Moreover, the continuous electrical charges do not represent the early atmosphere. There may have been some electricity in the clouds but not in this amount.
The last point is, that amino acids have even been found in meteorites. Thus, some scientits assume that amino acids were built by accident all the time and are not an enormous step in the evolution of life.
I have just taken a short look and there could still be some other mistakes.
I am a student and this is how I would correct some of your sentences.
All in all I think it is a very good text still you could at some facts about the endosymbiotic theory.
ps: Good look with your TOEFl exam :=)